Novartis said its experimental drug atrasentan was shown to have a positive effect on kidney function in people suffering from a rare type of kidney disease in an interim analysis of a late-stage drug trial. Treatment with the drug candidate, acquired as part of the purchase of U.S. biotech firm Chinook Therapeutics for up to $3.5 billion, resulted in a clinically meaningful improvement in kidney filtration in patients suffering from IgA nephropathy when compared to placebo, the Swiss drugmaker said in a statement.